It has been common practice to package low-viscosity liquids in pressure containers along with a propellant gas that ejects the contained liquid in a fine spray when a discharge valve is opened. This type of device, while used in tremendous quantities, has fallen into disfavor for two reasons:
(A) The cost of the propellant gas, and the necessary space occupied by it in the container, and
(B) THE ADVERSE ECOLOGICAL EFFECTS OF THE PROPELLANT GAS (FREON) MOST COMMONLY USED. Objections to the aerosol-type device have resulted in increased use of dispensers functioning in the manner of a small pump, usually actuated by finger-pressure, and operating directly on the liquid within the container. The pump and the aerosol systems are both limited to handling low-viscosity liquids.
A modification of the aerosol container has been proposed, which adds an inner readily deformable container for the liquid to be dispensed, and admits the gas pressure exclusively in the space between the inner and outer containers. This arrangement is really no answer to the problem, as the space for the gas is still roughly the same, and the ecological problem is not solved. Even though the propellant gas is not projected into the atmosphere during the use period of the container, the destruction of the container after it has been discarded ultimately releases the gas into the atmosphere. Aerosols, incidentally, are single-use devices, as there are no substantial salvage programs for them in general use at the time of the filing of this application. Pump devices are readily capable of re-use, and are commonly seen in conjunction with small containers of window-cleaning solution.